This invention pertains to apparatus for producing, in a magnetic image-storage medium, a high-resolution, smooth-edge-defining magnetic image. More particularly, it relates to the production of a generally doughnut-shaped magnetized region in such a medium, which region functions as a portion of a total magnetic image, with magnetization in the region characterized by multi-directionally oriented magnetic vectors distributed generally with spherical geometry. The magnetic field for producing the magnetized region is generated by the induction of magnetic flux by an electricity-conducting spiral coil spaced from the field.
For the purpose of illustration, embodiment of the invention are described herein in the setting of electromagnetic printers, wherein the invention has been found to have particular utility.
In recent years, there has been much interest in the development of electromagnetic printers. The basic operational mode for such a printer is that electromagnetic "writing heads" are used to create discrete magnetized regions in an expanse of a magnetic image-storage medium--thus to create the desired image--with this region then suitably coated with a magnetizable powdered toner which is later transferred in a variety of ways to a sheet of paper, or the like.
In the past, the individually magnetized regions which combine to form an overall image have been produced in two principal ways. One of these is referred to as linear perpendicular magnetizing, and the other as linear longitudinal magnetizing. The first of these prior art techniques produces a magnetized region through a pair of North-South poles disposed along an axis which is substantially normal to the plane of an image-storage medium. Such a technique results, predominantly, in normally directed magnetic vectors (relative to the plane of the medium) in the magnetized region. The second-mentioned technique uses a pair of confronting North-Sourth poles placed along one side, and parallel to the plane, of an image-storage medium. This technique produces a magnetized region with magnetic vectors directed substantially within a plane paralleling that of the medium.
Among the problems which have plagued apparatus employing each of these magnetizing techniques has been that the finally magnetized regions do not exhibit an especially high degree of toner-collecting capability, particularly in the zones between adjacent magnetized regions. As a consequence of this, edge definition in a resulting printed image is often quite poor. This becomes especially apparent in the printing of alpha/numeric characters whose edges can appear to be jagged rather than smooth and continuous.
One technique of which applicant is aware has been developed to overcome this problem is disclosed in U.S. Pat. No. 2,950,161 issued to W. J. Rueger, entitled "Coaxial Magnetic Printing Head". The invention therein described includes a cylindrical inner magnetic-flux-permeable core surrounded by an electrically conductive sleeve functioning as a single coil. The sleeve is in turn surrounded by an outer magnetic-flux-permeable base. When the sleeve is conducting, a magnetic field is produced between coplanar faces of the core and base across the sleeve.
Although this invention solves the above-described problem, it has other limitations. These limitations include the inherent interdependency between size of the coil and size of the resulting magnetic field. In brief, the field size is determined from the coil size.
Additionally, the amount of flux induced by the coil is limited to that provided by a single coil. In the Rueger patent, it appears that this is compensated for by increasing the size of the coil. This requires more power to operate and results in an enlarged magnetic field.
A general object of the present invention is to provide a unique apparatus for overcoming such deficiencies in a highly satisfactory, and relatively simple manner.
More specifically, an object of the invention is to provide such an apparatus which is capable of producing a magnetic image, in which individual magnetized regions exhibit a very high degree of toner-capturing capability, coupled with a propensity for the zones of adjacency between such regions also to exhibit high toner-collecting capacity.
Yet another object of the invention, and one which relates to the preceeding object, is to provide such an apparatus wherein extremely good edge definition (continuous smoothness) is attainable in the edges of a printed image.
It is a further and primary object of the invention to provide such a method and apparatus which divorces the size of the magnetic poles, and, therefore, the resulting field, from the coil inducing magnetic flux.
According to a preferred embodiment of the present invention, such magnetic imaging is accomplished through the cooperative action of two opposite-polarity concentric magnetic poles created by magnetic flux induced with a spiral coil spaced from the poles. These poles function to create, on a face in a magnetic storage medium, a somewhat doughnut-shaped magnetized zone, which zone is characterized by multi-directionally oriented magnetic vectors that are distributed generally with spherical geometry. By creating magnetized zones characterized by spherical magnetic-vector geometry, each individual zone exhibits an extremely high capacity for capturing toner. Further, immediately adjacent regions all experience confronting or opposing magnetic vectors, which results in the zones between adjacent regions also exhibiting high toner-collecting capability. With such geometry attained for each individual magnetized zone, and considering that a string of such zones will define the edge of an image, the toner-collecting capability exhibited in the indentations between adjacent zones avoids the development of a jagged edge in a finally printed image.
Also, by physically separating the magnetic field and the coil inducing the magnetic flux which creates the magnetic field, substantially reduced field sizes are available. The size limitation is then a constraint caused by construction methods rather than by coil requirements. The use of spiral coils also multiplies the effectiveness of the coil in inducing a desired amount of magnetic flux.
In order to explain the extreme versatility of the proposed invention, and after there is given below a general description of the basic apparatus required to perform the invention, several specific writing head constructions are described, which constructions have been shown to offer a high degree of utility. In each of these constructions, a generally coplanar concentric opposite-polarity pole configuration is used to achieve the desired doughnut-shaped magnetized region with spherical-geometry magnetic vectors.
Another important feature of the invention is that magnetic pole pairs having the desired geometry can be formed in extremely small regions within very thin-film versatile materials. As a consequence, very high-quality, high-resolution, low-power-consumption, and low-cost magnetic writing is made possible by the invention.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.